An RPi0W is used to control a home fan unit. Wifi is used to monitor the RPi0W and in a next phase, Wifi is needed to get the weather forecast. It is found that if the Wifi network is down for some time, the RPi0W often freezes at about the time the Wifi network becomes operational again.

The RPi0W is running the latest release of Raspbian Stretch Lite and there are currently no outstanding upgrades. Especially the wireless firmware release mentioned in viewtopic.php?t=203508 is included.

The last occurrence was on 2018.02.21. At about 07:02 the Wifi network became operational. However, the RPI0W could not be accessed through SSH, and it did not react on ping either. After a power cycle, the RPI0W becomes accessible. The various log files show entries up to the time that Wifi became operational. The messages in /var/log/syslog preceding the boot-messages are:

A second RPi0W, used for tests and development, shows the same behaviour. It is running Raspbian Stretch with desktop. Once frozen, the TV screen does receive a signal via HDMI, but the screen is black. The keyboard is not operational, as it does not receive power any more via the USB connection. Also on this RPi0W, the last messages in syslog before the boot messages are dated 2018.02.21 07:03, and are also messages from dhclient.

I've played with enabling / disabling IPv6 (which is not used in my home network). Only once one RPi0W with IPv6 enabled was still operational after Wifi was restored, but it turned out to be just a coincidence.

We are actively investigating this, both at Pi towers and the wireless chip supplier. It appears to be a problem with the latest release firmware, so rolling it back should fix the problem (but bring some other ones back).

Principal Software Engineer at Raspberry Pi (Trading) Ltd.
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On both RPi0W's a test is now running. Yesterday I've installed raspbian with kernel version 4.14.22, using `sudo rpi-update`. When the Wifi network became operational, this RPi0W restored it's wlan connection and did not freeze. The other RPi0W was frozen and needed a power-cycle to become accessible.

Today, a previous version of the firmware was installed on the second RPi0W, as described in the preceding post. (When I tried to get the firmware from share-online.biz, a pop-up appeared stating that I had won an IPhone. This website is now on my blacklist.) The RPi0W is rebooted. I'll report after the next Wifi outage.

Note that the 4.14.22 version includes the firmware released around 2018.02.07.

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The installation of an older version of the driver fixes my issue. The RPi0W became accessible after an outage of the Wifi network. Further tests with kernel 4.14.22 showed that that version on an RPi0W does NOT always becomes accessible after an outage of Wifi.
For the time time, as long as I do not hit one of the issues 'unsolved' by installing an older driver.

For the time being, as long as I do not hit one of the issues 'unsolved' by installing an older driver, my problem is solved.

I think the errors were more common if using the Pi as an access point, under certain circumstances. I was unable to replicate this "mailbox" issue that resulted, so it's not common. You should be OK.

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I'm using PI as an accesspoint with hostapd and old driver version. It works so far without errors. However I don't use it excessively. It's only an access to the pi for a few command line options and streaming raspi camera video for some minutes.

I am encountering the same problem with two rasberrypi3 with newest rasbian stretch and internal Wifi, When I reboot my router the Pi looses wifi connection, when wifi is back on the Pi freezes and need to be restarted with a power cycle. My Pi's are configured with static ip, problem is the same when ip is assigned by dhcp.

Does this apply only to the rpi0w? What about other pis? Are they affected too?

All Pi's with wireless since they all use the same wireless chip and firmware.

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The issue is long fixed with official binaries. I use a few PIs (3 and Zero W) in Wifi and none freezes.

A Pi Zero W is working for month stable. Data is requested over Wifi every minute. It also fetches data every minute.

How do you know the system freezes? Did you connect via serial console to see if PI is still up? I suspect some kind of incompability with PI and your Wifi hardware. Some APs make quite a lot trouble, not only with PIs.

To test if that particular issue is affecting you: Connect PI to Wifi, then reboot AccessPoint. If PI never connects again it is likely this issue. But as I said, this issue is long gone for me.

On two of the ZeroWs I've installed the UFL socket to improve wifi signal - this makes no difference to the failure, although signal quality is much improved.

Symptoms:

On boot, about 20% of the time it does not connect to wifi.
On a successful boot the OS hangs after 20 mins - 3 hours.

After boot the system is idle with just another machine pinging it every second to track whether it is active on wifi
Wifi power management is disabled in rc.local

OS hang means:
- does not respond to USB keyboard
- disconnects from wifi and cannot be pinged
- HDMI is active showing no error messages
- nothing interesting in syslog or kernel log following a power cycle